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--Column ID of table A is primary key:
CREATE TABLE A (
ID int4 not null
);
CREATE UNIQUE INDEX AI ON A (ID);
--Columns REFB of table B and REFC of C are foreign keys referencing ID of A:
CREATE TABLE B (
REFB int4
);
CREATE INDEX BI ON B (REFB);
CREATE TABLE C (
REFC int4
);
CREATE INDEX CI ON C (REFC);
--Trigger for table A:
CREATE TRIGGER AT BEFORE DELETE OR UPDATE ON A FOR EACH ROW
EXECUTE PROCEDURE
check_foreign_key (2, 'cascade', 'ID', 'B', 'REFB', 'C', 'REFC');
/*
2 - means that check must be performed for foreign keys of 2 tables.
cascade - defines that corresponding keys must be deleted.
ID - name of primary key column in triggered table (A). You may
use as many columns as you need.
B - name of (first) table with foreign keys.
REFB - name of foreign key column in this table. You may use as many
columns as you need, but number of key columns in referenced
table (A) must be the same.
C - name of second table with foreign keys.
REFC - name of foreign key column in this table.
*/
--Trigger for table B:
CREATE TRIGGER BT BEFORE INSERT OR UPDATE ON B FOR EACH ROW
EXECUTE PROCEDURE
check_primary_key ('REFB', 'A', 'ID');
/*
REFB - name of foreign key column in triggered (B) table. You may use as
many columns as you need, but number of key columns in referenced
table must be the same.
A - referenced table name.
ID - name of primary key column in referenced table.
*/
--Trigger for table C:
CREATE TRIGGER CT BEFORE INSERT OR UPDATE ON C FOR EACH ROW
EXECUTE PROCEDURE
check_primary_key ('REFC', 'A', 'ID');
-- Now try
INSERT INTO A VALUES (10);
INSERT INTO A VALUES (20);
INSERT INTO A VALUES (30);
INSERT INTO A VALUES (40);
INSERT INTO A VALUES (50);
INSERT INTO B VALUES (1); -- invalid reference
INSERT INTO B VALUES (10);
INSERT INTO B VALUES (30);
INSERT INTO B VALUES (30);
INSERT INTO C VALUES (11); -- invalid reference
INSERT INTO C VALUES (20);
INSERT INTO C VALUES (20);
INSERT INTO C VALUES (30);
DELETE FROM A WHERE ID = 10;
DELETE FROM A WHERE ID = 20;
DELETE FROM A WHERE ID = 30;
SELECT * FROM A;
SELECT * FROM B;
SELECT * FROM C;